Systems and methods for handoff of a mobile telephone call in a VOIP environment

ABSTRACT

When a mobile telephony device is conducting a voice over Internet protocol (VOIP) telephone call via a data network, and the mobile telephone device transitions from a first wireless data connection to a second wireless data connection, signaling between the mobile telephone device and a media relay inform the media relay how to address data packets bearing the media of the call after the transition has occurred. In some embodiments, the mobile telephone device establishes multiple simultaneous wireless data connections, and the mobile telephony device switches the media of the call between the wireless data connections depending on the quality of the wireless data connections.

This application is a continuation of U.S. application Ser. No.13/324,666, filed on Dec. 13, 2011, now issued as U.S. Pat. No.8,223,720, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The invention is related to Internet protocol (IP) telephony systemsthat allow users to place and receive telephone calls, and to send andreceive text and video messages via data packets that are communicatedover a data network.

A mobile telephony device conducts a voice over Internet protocol (VOIP)telephone call by linking itself to a data network using a wireless dataconnection. The wireless data connection could be a link to a wirelessrouter that is coupled to a data network, such as a WiFi or WiMaxrouter. Alternatively, a mobile telephony device could establish awireless data connection to a data network over a data channel providedby a cellular telephony service provider.

If a mobile telephony device is conducting a VOIP telephone call, andthe user of the mobile telephony device moves out of communication rangeof the wireless router or cell tower that the mobile telephony devicehas used to establish a wireless data connection, the call will bedisconnected. However, it is also possible that the movement of themobile telephony device will bring the mobile telephony device withincommunication range of a new wireless router or cell tower at the sametime, or before, the mobile telephony device passes out of communicationrange of the first wireless router or cell tower. If this occurs, itwould be desirable for the mobile telephony device to automaticallyestablish a new wireless data connection with the new wireless router orcell tower, and for the call to continue through the new wireless dataconnection.

Unfortunately, it is difficult to transition a VOIP telephone call froma first wireless data connection to a second wireless data connectionmid-call. During a VOIP telephone call, the mobile telephony device issending data packets to and receiving data packets from a specificserver, gateway or media relay in the data network. During call setup,the server, gateway or media relay will have been provided with theInternet protocol (IP) address and port number that data packets must besent to in order to arrive at the mobile telephony device. Likewise, theserver, gateway or media relay will expect to receive all data packetssent from the mobile telephony device from that same IP address and portnumber during the entire telephony session.

If the mobile telephony device transitions from a first wireless dataconnection to a second wireless data connection, the IP address and portnumber associated therewith are both likely to change. The mobiletelephony device will still have the IP address and port number of theserver, gateway or media relay that it has been communicating with, butit will be sending data packets bearing the media of the call to theserver, gateway or media relay from its new IP address and port number.These data packets will not be recognized by the server, gateway ormedia relay as coming from the proper location. As a result, the datapackets will be ignored. Likewise, the server, gateway or media relaywill not know to re-direct data packets intended for the mobiletelephony device to the new IP address and port number now being used bythe mobile telephony device to continue the telephony session. For thesereasons, it is difficult, or impossible, for a mobile telephony deviceconducting a VOIP telephone call to transition from a first wirelessdata connection to a second wireless data connection mid-call.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a communications environment including variouselements which are associated with an Internet protocol (IP) telephonysystem operating in accordance with the invention;

FIG. 2 is a block diagram of various elements of a processor that formspart of an IP telephony system operating in accordance with theinvention;

FIG. 3 is a block diagram illustrating the path that data packetsbearing call setup signaling and the media of a VOIP telephone calltraverse from a first telephone device to a second telephony device;

FIG. 4 is a flowchart of steps of a first method embodying the inventionthat would be performed by a mobile telephony device to accomplish atransition from a first wireless data connection to a second wirelessdata connection during a VOIP telephone call;

FIG. 5 is a flowchart of a second method embodying the invention thatwould be performed by a mobile telephony device to accomplish atransition from a first wireless data connection to a second wirelessdata connection during a VOIP telephone call;

FIG. 6 is a flowchart of a third method embodying the invention in whichmultiple wireless data connections are established by a mobile telephonydevice and where the media of a VOIP telephone call is switched betweenthe wireless data connections during the duration of the call;

FIG. 7 is a block diagram illustrating elements of an IP communicationsystem embodying the invention; and

FIG. 8 is a block diagram illustrating elements of a media relaycommunication system embodying the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description of preferred embodiments refers tothe accompanying drawings, which illustrate specific embodiments of theinvention. Other embodiments having different structures and operationsdo not depart from the scope of the present invention.

In the following description, the terms VOIP system, VOIP telephonysystem, IP system and IP telephony system are all intended to refer to asystem that connects callers and that delivers data, text and videocommunications using Internet protocol data communications.

As illustrated in FIG. 1, a communications environment 100 is providedto facilitate IP enhanced communications. An IP telephony system 120enables connection of telephone calls between its own customers andother parties via data communications that pass over a data network 110.The data network 110 is commonly the Internet, although the IP telephonysystem 120 may also make use of private data networks. The IP telephonysystem 120 is connected to the Internet 110. In addition, the IPtelephony system 120 is connected to a publicly switched telephonenetwork (PSTN) 130 via a gateway 122. The PSTN 130 may also be directlycoupled to the Internet 110 through one of its own internal gateways(not shown). Thus, communications may pass back and forth between the IPtelephony system 120 and the PSTN 130 through the Internet 110 via agateway maintained within the PSTN 130.

The gateway 122 allows users and devices that are connected to the PSTN130 to connect with users and devices that are reachable through the IPtelephony system 120, and vice versa. In some instances, the gateway 122would be a part of the IP telephony system 120. In other instances, thegateway 122 could be maintained by a third party.

Customers of the IP telephony system 120 can place and receive telephonecalls using an IP telephone 108 that is connected to the Internet 110.Such an IP telephone 108 could be connected to an Internet serviceprovider via a wired connection or via a wireless router. In someinstances, the IP telephone 108 could utilize the data channel of acellular telephone system to access the Internet 110.

Alternatively, a customer could utilize a analog telephone 102 which isconnected to the Internet 110 via a telephone adapter 104. The telephoneadapter 104 converts analog signals from the telephone 102 into datasignals that pass over the Internet 110, and vice versa. Analogtelephone devices include but are not limited to standard telephones anddocument imaging devices such as facsimile machines. A configurationusing a telephone adapter 104 is common where the analog telephone 102is located in a residence or business. Other configurations are alsopossible where multiple analog telephones share access through the sameIP adaptor. In those situations, all analog telephones could share thesame telephone number, or multiple communication lines (e.g., additionaltelephone numbers) may provisioned by the IP telephony system 120.

In addition, a customer could utilize a soft-phone client running on acomputer 106 to place and receive IP based telephone calls, and toaccess other IP telephony systems (not shown). In some instances, thesoft-phone client could be assigned its own telephone number. In otherinstances, the soft-phone client could be associated with a telephonenumber that is also assigned to an IP telephone 108, or to a telephoneadaptor 104 that is connected one or more analog telephones 102.

Users of the IP telephony system 120 are able to access the service fromvirtually any location where they can connect to the Internet 110. Thus,a customer could register with an IP telephony system provider in theU.S., and that customer could then use an IP telephone 108 located in acountry outside the U.S. to access the services. Likewise, the customercould also utilize a computer outside the U.S. that is running asoft-phone client to access the IP telephony system 120.

A third party using an analog telephone 132 which is connected to thePSTN 130 may call a customer of the IP telephony system 120. In thisinstance, the call is initially connected from the analog telephone 132to the PSTN 130, and then from the PSTN 130, through the gateway 122 tothe IP telephony system 120. The IP telephony system 120 then routes thecall to the customer's IP telephony device. A third party using acellular telephone 134 could also place a call to an IP telephony systemcustomer, and the connection would be established in a similar manner,although the first link would involve communications between thecellular telephone 134 and a cellular telephone network. For purposes ofthis explanation, the cellular telephone network is considered part ofthe PSTN 130.

In the following description, references will be made to an “IPtelephony device.” This term is used to refer to any type of devicewhich is capable of interacting with an IP telephony system to completean audio or video telephone call or to send and receive text messages,and other forms of communications. An IP telephony device could be an IPtelephone, a computer running IP telephony software, a telephone adapterwhich is itself connected to a normal analog telephone, or some othertype of device capable of communicating via data packets. An IPtelephony device could also be a cellular telephone or a portablecomputing device that runs a software application that enables thedevice to act as an IP telephone. Thus, a single device might be capableof operating as both a cellular telephone and an IP telephone.

The following description will also refer to a mobile telephony device.The term “mobile telephony device” is intended to encompass multipledifferent types of devices. In some instances, a mobile telephony devicecould be a cellular telephone. In other instances, a mobile telephonydevice may be a mobile computing device, such as the Apple iPhone™, thatincludes both cellular telephone capabilities and a wireless datatransceiver that can establish a wireless data connection to a datanetwork. Such a mobile computing device could run appropriateapplication software to conduct VOIP telephone calls via a wireless dataconnection. Thus, a mobile computing device, such as an Apple iPhone™, aRIM Blackberry or a comparable device running Google's Android operatingsystem could be a mobile telephony device.

In still other instances, a mobile telephony device may be a device thatis not traditionally used as a telephony device, but which includes awireless data transceiver that can establish a wireless data connectionto a data network. Examples of such devices include the Apple iPodTouch™ and the iPad™. Such a device may act as a mobile telephony deviceonce it is configured with appropriate application software.

FIG. 1 illustrates that a mobile computing device with cellularcapabilities 136 is capable of establishing a first wireless dataconnection A with a first wireless access point 140, such as a WiFI orWiMax router. The first wireless access point 140 is coupled to theInternet 110. Thus, the mobile computing device 136 can establish a VOIPtelephone call with the IP telephony system 120 via a path through theInternet 110 and the first wireless access point 140.

FIG. 1 also illustrates that the mobile computing device 136 canestablish a second wireless data connection B with a second wirelessaccess point 142 that is also coupled to the Internet 110. Further, themobile computing device 136 can establish a third wireless dataconnection C via a data channel provided by a cellular service provider130 using its cellular telephone capabilities. The mobile computingdevice 136 could also establish a VOIP telephone call with the IPtelephony system 120 via the second wireless connection B or the thirdwireless connection C.

Although not illustrated in FIG. 1, the mobile computing device 136 maybe capable of establishing a wireless data connection to a data network,such as the Internet 110, via alternate means. For example, the mobilecomputing device 136 might link to some other type of wireless interfaceusing an alternate communication protocol, such as the WiMax standard.

FIG. 2 illustrates elements of a computer processor 150 that can be usedas part of the IP telephony system 120 to accomplish various functions.The IP telephony system 120 could include multiple processors 150located at various locations in the system, along with their operatingcomponents and programming, each carrying out a specific or dedicatedportion of the functions performed by the VOIP based telephony service120.

The processor 150 shown in FIG. 2 may be one of any form of a generalpurpose computer processor used in accessing an IP-based network, suchas a corporate intranet, the Internet or the like. The processor 150comprises a central processing unit (CPU) 152, a memory 154, and supportcircuits 156 for the CPU 152. The processor 150 also includes provisions158/160 for connecting the processor 150 to customer equipment and toservice provider agent equipment, as well as possibly one or moreinput/output devices (not shown) for accessing the processor and/orperforming ancillary or administrative functions related thereto. Theprovisions 158/160 are shown as separate bus structures in FIG. 2;however, they may alternately be a single bus structure withoutdegrading or otherwise changing the intended operability of theprocessor 150.

The memory 154 is coupled to the CPU 152. The memory 154, orcomputer-readable medium, may be one or more of readily available memorysuch as random access memory (RAM), read only memory (ROM), floppy disk,hard disk, flash memory or any other form of digital storage, local orremote, and is preferably of non-volatile nature. The support circuits156 are coupled to the CPU 152 for supporting the processor in aconventional manner. These circuits include cache, power supplies, clockcircuits, input/output circuitry and subsystems, and the like.

A software routine 162, when executed by the CPU 152, causes theprocessor 150 to perform processes of the disclosed embodiments, and isgenerally stored in the memory 154. The software routine 162 may also bestored and/or executed by a second CPU (not shown) that is remotelylocated from the hardware being controlled by the CPU 152. Also, thesoftware routines could also be stored remotely from the CPU. Forexample, the software could be resident on servers and memory devicesthat are located remotely from the CPU, but which are accessible to theCPU via a data network connection.

The software routine 162, when executed by the CPU 152, transforms thegeneral purpose computer into a specific purpose computer that performsone or more functions of the IP telephony system 120. Although theprocesses of the disclosed embodiments may be discussed as beingimplemented as a software routine, some of the method steps that aredisclosed therein may be performed in hardware as well as by a processorrunning software. As such, the embodiments may be implemented insoftware as executed upon a computer system, in hardware as anapplication specific integrated circuit or other type of hardwareimplementation, or a combination of software and hardware. The softwareroutine 162 of the disclosed embodiments is capable of being executed onany computer operating system, and is capable of being performed usingany CPU architecture.

When a VOIP telephone call is to be established with a mobile telephonydevice, the mobile telephony device must first have a wireless dataconnection to a data network so that data packets can be communicated toand from the mobile telephony device to setup the call, and to carry themedia of the call. FIG. 3 illustrates a mobile telephony device withcellular capabilities 136 that can establish a wireless data connectionwith a first wireless access point 140, a second wireless access point142 or through a data channel provided by a cellular service provider170. FIG. 3 also illustrates the different paths that data packetsbearing call setup signaling and data packets bearing the media of acall may traverse over the various elements used to setup and carry aVOIP telephone call. In FIG. 3, solid lines indicate the paths traversedby data packets bearing call setup signaling, and dashed lines indicatethe paths traversed by data packets bearing the media of a call.

The embodiment illustrated in FIG. 3 presumes that an analog telephone132 will be used by a calling party to place a call to the mobilecomputing device 136. The calling party's analog telephone 132 isconnected to a PSTN 130. The PSTN 130, in turn, is connected to agateway 122, which allows the PSTN 130 to communicate with a IPtelephony system 120. The IP telephony system 120 can communicate withthe mobile computing device 136 via any one of multiple wireless dataconnections provided through the first wireless access point 140, thesecond wireless access point 142 and the cellular service provider 170.

When the calling party dials the telephone number of the mobilecomputing device 136 on his analog telephone 132, call setup signalingis communicated to the PSTN 130, and then from the PSTN 130 to the IPtelephony system 120 via the gateway 122. The call setup signaling isreceived by an inbound proxy server 310 of the IP telephony system. TheIP telephony system then checks to determine if the mobile computingdevice 136 is available via a wireless data connection, which would makeit possible to setup a VOIP call to the mobile computing device 136.

Typically, if the mobile computing device 136 is configured to receiveVOIP telephone calls from the IP telephony system 120, each time thatthe mobile computing device 136 establishes a wireless data connection,the mobile computing device 136 conducts a registration process with theIP telephony system 120. During the registration process, the IPtelephony system 120 is informed of the IP address and port number atwhich the mobile computing device 136 can be reached. Thereafter, datais periodically communicated between the mobile computing device 136 andthe IP telephony system 120 to keep this wireless data connection open.

In one embodiment of the invention, the mobile computing device 136establishes a wireless data connection via path A through the firstwireless access point 140 associated with a first location. Once thatwireless data connection is established, the mobile telephony device 136registers with the IP telephony system 120 via data communicationspassing over the first wireless access point 140. The data packetsbearing those communications which are received by the IP telephonysystem 120 would be coming from the first wireless access point 140, andthey would bear the IP address of the wireless access point, andpossibly a port number that was assigned to the mobile telephony device.However, some type of network address translation scheme might also byused by the wireless access point. Regardless, the IP telephony systemwill be informed of the IP address and port number to which data packetsmust be addressed to ensure the data packets are ultimately delivered tothe mobile computing device 136 via the first wireless access point 140.Thereafter, the IP telephony system 120 will address all data packetsdestined for the mobile computing device 136 to that address and portnumber. Also, the IP telephony system 120 will expect to receive datapackets sent from the mobile computing device 136 to be sent from thatsame IP address and port number.

Continuing with the call setup explanation, when call signalingrequesting the call is received by the inbound proxy server 310 of theIP telephony system 120, the IP telephony system checks to determine ifthe mobile computing device 136 is registered. If so, the IP telephonysystem knows how to reach the mobile computing device 136 to setup andcarry the call. In this instance, an outbound proxy server 320 of the IPtelephony system 120 sends data packets bearing call setup signaling tothe first wireless access point 140, via the Internet 110, using theaddress information it acquired for the mobile computing device 136 whenthe mobile computing device registered with the IP telephony system 120.Those data packets are then delivered to the mobile computing device 136by the first wireless access point 140.

In some instances, the path traversed by data packets that bear callsetup signaling will be the same as the path traversed by data packetsbearing the media of the call. However, in the following description amedia relay of the IP telephony system 120 is used to convey datapackets bearing the media of the call between the calling party and thecalled party's telephony device. As a result, the path traversed by datapackets bearing the media of the call will be different from the pathtraversed by data packets bearing the call setup signaling.

During call setup, the IP telephony system 120 will select a media relaythat will be used to help communicate data packets bearing the media ofthe call. In one embodiment of the invention, the IP telephony system120 designates a first media relay 330. Of course in other instances,the second media relay 332 could be used instead. This information willbe communicated to the mobile computing device 136 during call setup. Asa result, once call setup is complete, the mobile computing device 136will send data packets bearing the media of the call to the first mediarelay 330, and the first media relay will forward the data packets tothe gateway 122 so that they can be delivered as audio to the callingparty's telephony device 132 via the PSTN 130. Likewise, the first mediarelay 330 will send data packets bearing the media of the call to themobile computing device 136 by addressing the data packets to theaddress established for the mobile computing device 136 when the mobilecomputing device registered with the IP telephony system 120. Asdescribed above, this will be an address associated with the firstwireless access point 140.

Once the call commences, data packets bearing the media of the call willpass back and forth along a path that includes the gateway 122, thefirst media relay 330, and the first wireless access point 140. So longas the mobile computing device 136 maintains wireless data connection Athrough the first wireless access point 140, the call continues.However, if the mobile computing device moves from the first location toa second location that is too far away from the first wireless accesspoint 140 to maintain wireless data connection A, wireless connection Ais lost. However, the mobile computing device 136 is able to establishwireless data connection B with the second wireless access point 142which is associated with the second location. The mobile computingdevice continues the telephone call established with the calling party'stelephone 132 from the second location over the second wireless dataconnection B established with the second wireless access point 142.

As explained above, the first media relay 330 expects to receive datapackets generated by the mobile computing device 136 and bearing mediaof the call from the address of the first wireless access point 140, aswas established at the beginning of the call. If the mobile computingdevice 136 begins sending data packets bearing the media of the call tothe first media relay 330 from the second wireless access point 142,which has a different address, and in the absence of further action, thefirst media relay 330 will not recognize the data packets as relating tothe same telephone call. Because the data packets are originating from anew and unrecognized address, the data packets would be ignored. Thesubject invention provides a way to inform the first media relay 330that the mobile computing device 136 has transitioned to a new wirelessdata connection. Methods embodying the invention provide the media relaywith the new address to which the first media relay 330 should send datapackets.

In methods embodying the invention, a certificate is established for thecall during call setup. A copy of the certificate is temporarily storedon the mobile computing device 136 for the duration of the call. Thecertificate could be generated by the IP telephony system 120, or by themobile computing device 136, or by some other element of the system. Acopy of the certificate is also communicated to the first media relay330. This could occur during call setup, or it could occur when themobile computing device 136 begins to communicate media data packets tothe first media relay 136. The certificate could be sent to the firstmedia relay 330 from the mobile computing device 136, or from an elementof the IP telephony system 120. Regardless, the first media relay 330also stores a copy of the certificate for the duration of the call.Procedures for generating and verifying call certificates are well knownto those of ordinary skill in the art. Also, in some embodiments, thecall certificates may be encrypted before they are sent from one elementto the next to prevent interception and unauthorized use of the networkelements.

If the mobile computing device 136 transitions from a first wirelessdata connection to a second wireless data connection during the pendencyof a call, the mobile computing device 136 sends the call certificate tothe first media relay 330 via the second wireless data connection B aspart of an initial contact made through the second wireless dataconnection B. This informs the first media relay 330 that the mobilecomputing device has transitioned to the second wireless data connectionB passing through the second wireless access point 142, and that thecall can continue over this new wireless data connection. Thiscommunication also provides the first media relay 330 with the addressto which data packets bearing the media of the call should be sent sothat the data packets can reach the mobile computing device 136 throughthe second wireless data connection B. The new address will be anaddress associated with the second wireless access point 142. After thefirst media relay 330 has this information, the first media relay 330will know to send data packets to the new address, and also to acceptdata packets sent by the mobile computing device 136 which appear tooriginate from the new address associated with the second wirelessaccess point 142. Thus, the call can continue over the second wirelessdata connection B.

The same type of transition could occur if the mobile computing deviceswitches from the second wireless data connection B established throughthe second wireless access point 142 to a third wireless data connectionC which is established over a data channel provided by the cellularservice provider 170. The same basic process would occur to inform thefirst media relay 330 of the change. Likewise, the same procedures wouldbe followed if the mobile computing device transitions from a wirelessdata connection established via a data channel provided by a cellularservice provider to a new wireless data connection established through awireless router.

FIG. 4 illustrates steps of a method embodying the invention whichallows a mobile computing device 136 to transition from a first wirelessdata connection to a second wireless data connection. The method beginsin step S402 when the mobile computing device 136 conducts call setupsignaling with an outbound proxy server 320 of the IP telephony system120. This signaling reaches the mobile computing device 136 via awireless data connection the mobile computing device 136 hasestablished, as discussed earlier. For purposes of explanation, themobile computing device 136 has established wireless data connection Bthrough the second wireless access point 142, as shown in FIG. 3. Duringthis initial call setup signaling, the mobile computing device 136receives a certificate for the call. Also, a media relay for the callwould be identified. In this embodiment, the second media relay 332 hasbeen selected for the call.

In step S404, the mobile computing device 136 begins to communicate datapackets bearing the media of the call with the second media relay 332via wireless data path B, through the second wireless access point 142.In step S406, a check is performed to determine if the call has beenterminated. If so, the call ends. If not, a check is performed in stepS408 to determine if the mobile computing device has transitioned to anew wireless data connection. If not, the method loops back to stepS404, and communications continue with the second media relay 332 overwireless data connection B through the second wireless access point 142.

If, during one of the checks performed in step S408, the mobilecomputing device determines that a transition to a new wireless dataconnection has occurred, the method proceeds to step S410, where themobile computing device 136 contacts the second media relay 332 over thewireless data connection, such as wireless data connection C, and sendsthe second media relay 332 a copy of the certificate for the call. Thisinforms the second media relay 332 of the occurrence of the transition,it informs the second media relay 332 that this is a continuation of theoriginal call, and that the second media relay should now send datapackets to a new address and port number associated with the cellularservice provider 170. This also informs the second media relay 332 toexpect data packets transmitted from the mobile computing device 136 tohave the new address and port number associated with the cellularservice provider 170.

In step S412, the mobile computing device 136 communicates data packetswith the second media relay 332 over wireless data connection C, whichpasses over the cellular service provider 170. Next, in step S414 acheck is performed to determine if either party has terminated the call.If so, the call ends. If not, a check is performed in step S416 todetermine if another transition to another wireless data connection hasoccurred. If not, the call proceeds as the mobile computing device 136continues to communicate with the second media relay 332 over wirelessdata connection C. If another transition has occurred, the methodproceeds to step S410, where the mobile computing device 136 once againgoes through the process of informing the second media relay 332 of thetransition to a new wireless data connection.

In some instances, the transition from a first wireless data connectionto a second wireless data connection will consume enough time that theparties to the call might notice a break in communications. This couldoccur because of the time required for the mobile computing device toterminate the first wireless data connection and establish the secondwireless data connection. This could also be due to the time required toaccomplish the signaling with the media relay to inform the media relayof the change.

To help minimize or eliminate any interruption in the call that might benoticed by the parties to the call, it is possible for the mobilecomputing device to create a buffer of audio data for the call. Thebuffer would store a few seconds worth of audio that could be played tothe user of the mobile computing device during the transition. Likewise,the media relay involved in the call could buffer a few seconds of audiothat could be played to the calling party's telephone 132 during thetransition. The buffer(s) containing audio data could be built up overtime as the call proceeds.

In other embodiments, a message may be played to the parties to the callduring a transition to inform them to hold for a few moments. This wouldgive the system time to complete the transition from a first wirelessdata connection to a second wireless data connection. A second messagemight also be played to the parties once the transition is complete andthe call can resume.

The mobile computing device 136 could determine that there is a need fora call buffer to cover a wireless data connection transition bymonitoring the quality of the existing wireless data connection. Forexample, the mobile computing device 136 could monitor the signalstrength of the connection to a wireless router or to a cell tower. Themobile computing device 136 might also monitor data packet transmissionstatistics to determine the strength or quality of the wireless dataconnection.

If the quality of the wireless data connection is already low, themobile computing device would determine that an audio buffer isdesirable. Likewise, if the quality is steadily declining over time, thedecline could indicate that the mobile computing device is moving awayfrom the wireless router or cell tower to which it is connected,indicating that a transition may be imminent. In these cases, the mobilecomputing device 136 establishes an audio buffer if one did not alreadyexist. The mobile computing device 136 might also act to increase thesize of an existing buffer to help cover an interruption that wouldoccur during a transition to a new wireless data connection.

The media relay handling the call will not have a way of independentlymeasuring the quality of the data connection being provided by theexisting wireless data connection established for the mobile computingdevice 136. However, if the mobile computing device 136 determines thatthe quality of its wireless data connection is poor, or is steadilydeclining, the mobile computing device 136 could inform the media relayof this fact so that the media relay could also establish an audiobuffer and/or increase the size of an existing audio buffer to preparefor a transition to a new wireless data connection.

FIG. 5 illustrates steps of another method embodying the invention wherean audio buffer for a call is created or increased in size because themobile computing device has determined that a transition to a newwireless data connection may be imminent. The method begins in stepS502, where a mobile computing device 136 conducts call setup signalingand receives a certificate for the call. The mobile computing device 136then begins to communicate data packets bearing the media of the callwith a media relay over a first wireless data connection.

In step S504, the mobile computing device 136 monitors the quality ofthe first wireless data connection. This can include conducting any ofthe quality measures of the wireless data connection discussed above, aswell as any other measures that are indicative of the strength orquality of the wireless data connection.

In step S506, a check is performed to determine if one of the parties tothe call has terminated the call. If so, the call ends. If not, themethod proceeds to step S508 where the mobile computing devicedetermines if a transition to a new wireless data connection appearsimminent. This judgment could be made if the quality of the wirelessdata connection is low, or if the quality appears to be steadilydeclining, indicating that the mobile computing device is moving awayfrom the device offering the wireless data connection.

If it appears that a transition to a new wireless data connection is notimminent, the method loops back to step S504, and the call continues. Ifit appears that a transition to a new wireless data connection isimminent, the method proceeds to step S510, where a new audio buffer isestablished, or where an existing audio buffer is made larger. Also,audio data is loaded into the buffer to fill the buffer, as much as ispossible. Step S510 could also include the mobile computing devicecontacting the media relay to inform the media relay that a transitionis imminent so that the media relay can create or enlarge and fill asimilar buffer at its end.

In step S512, a transition from the first wireless data connection to asecond wireless data connection would occur, according to the proceduresexplained above. During that transition, audio data from the bufferwould be played to the user of the mobile computing device 136. Also,the media relay may play audio data from its buffer to the other partyto the call. Then, in step S514, the mobile computing device would beginto communicate data packets bearing the media of the call with the mediarelay over the second wireless data connection. The method then loopsback to step S504.

Another strategy for dealing with a mobile computing device that ismoving into and out of range of multiple wireless data connection pointsis to have the mobile computing device 136 establish multiple wirelessdata connections to multiple wireless routers, or to one or more celltowers that can provide a data channel via cellular service. The mobilecomputing device monitors the quality provided by each of the wirelessdata connections, and the mobile computing device utilizes the wirelessdata connection having the highest quality to communicate the datapackets bearing the media of a call.

The mobile computing device would begin to communicate with the mediarelay over a first wireless data connection that offers the highestquality. If the first wireless data connection declines in quality tothe point where a second wireless data connection offers better quality,the mobile computing device then begins to communicate with the mediarelay over the second wireless data connection. The procedures explainedabove would be used to inform the media relay when a transition occurs.

If, during a call, the mobile computing device moves to within range ofa new device offering a new wireless data connection, the mobilecomputing device will go ahead and establish a new wireless dataconnection with the new device, even through the call may continue torun through one of the existing wireless data connections. The point isfor the mobile computing device to maintain multiple wireless dataconnections simultaneously so that the media bearing the audio of a callcan be transmitted through whichever wireless data connection offers thebest quality at any given moment. And the call can be transitioned fromone wireless data connection to another via the procedures explainedabove.

A method embodying the invention that includes maintaining multiplewireless data connections simultaneously is illustrated in FIG. 6. Themethod begins in step S602 where a new call is setup with a mobilecomputing device. The mobile computing device also sets up wireless dataconnections with any devices that offer such a connection.

In step S604, the mobile computing device communicates data packetsbearing the media of a call with a media relay over a first wirelessdata connection that offers the best quality among all availablewireless data connections. The method proceeds to step S606 where acheck is performed to determine if either party to the call hasterminated the call. If so, the call ends. If not, the method proceedsto step S608 where a check is made to determine if the mobile computingdevice should switch from the first wireless data connection to analternate wireless data connection. This could involve monitoring thequality provided by all available wireless data connections, anddetermining if one of the unused wireless data connections offerssignificantly better quality than the wireless data connection currentlyin use. If not, the method loops back to step S604. If so, the methodproceeds to step S610.

In step S610, the mobile computing device switches the call from thefirst wireless data connection to a new wireless data connection thatoffers better quality. The transition is handled using the methodsdiscussed above. Then, in step S612, the mobile computing device beginscommunicating data packets bearing the media of a call with the mediarelay over the new wireless data connection.

In step S614 a check is performed to determine if either party hasterminated the call. If so, the call ends. If not, the method proceedsto step S616 where another check is performed to determine if the callshould be switched to a new wireless data connection. If not, the methodloops back to step S612. If so, the method loops lack to step S610 sothat the transition can be accomplished.

Although the methods described immediately above involve keepingmultiple wireless data connections open simultaneously, the idlewireless data connections that are not being used to communicate themedia of the call will use up very little bandwidth. Thus, maintainingmultiple simultaneous wireless data connection will not consume a greatdeal of system capacity.

In the examples discussed above, when the call quality provided by afirst wireless data connection deteriorates, the call is switched to asecond wireless data connection. In alternate embodiments, when a secondwireless data connection is established between the telephony device andthe media relay, data packets bearing the audio of the call could becommunicated between the telephony device and the media relay inparallel via both the first and second wireless data connections. Inthis instance, if it becomes necessary to switch between the first andsecond wireless data connections, the media relay could simply stopusing the data packets being provided via the first wireless dataconnection and begin using the data packets provided via the secondwireless data connection. This could result in a faster transitionbetween the first and second wireless data connections.

If two simultaneous wireless data connections are established between atelephony device and a media relay, more data traffic must be carried bythe network. The parallel streams of data packets traversing the firstand second wireless data connections basically duplicate one another.For this reason, and to minimize the data traffic, the second wirelessdata connection and the parallel streaming of data packets may only beinitiated when the quality offered by the first wireless data connectionbegins to deteriorate.

In the foregoing examples, the quality offered by a wireless dataconnection is monitored. In some embodiments, this could comprisemeasuring and/or monitoring data packet transmission statistics. Inalternate embodiments, this could comprise measuring and/or monitoringthe voice or audio quality using methods that are well known to those ofordinary skill in the art.

All of the foregoing examples referred to a call. The call could be anaudio call or a video call. Thus, any references to an audio bufferwould apply equally to a buffer used hold video data.

Also, although the examples provided above referred to a mobilecomputing device, any type of mobile telephony device could be used inthe methods.

FIG. 7 illustrates elements of an IP communication system 700 embodyingthe invention and capable of performing the methods discussed above. TheIP communication system 700 includes a wireless communication unit 702that establishes a wireless data connection to a data network. In someembodiments, the wireless communication unit is capable of establishingand simultaneously maintaining multiple wireless data connections withthe data network.

The IP communication system 700 also includes a media communication unit704 that communicates with a media relay over a wireless data connectionto exchange data packets bearing the media of a VOIP telephone call, orsome other type of IP communication. Also, a certificate communicationunit 706 sends a certificate identifying a VOIP telephone call to themedia relay whenever a transition is made between first and secondwireless data connections.

In some embodiments, the IP communication system 700 also includes aquality monitoring unit 708 that monitors a quality of a wireless dataconnection. The IP communication system 700 may also include a switchingunit 710 that performs the functions needed to switch the mediacommunication unit 704 from a first wireless data connection to a secondwireless data connection so that data packets bearing the media of aVOIP call are communicated with the media relay over the second wirelessdata connection. This could occur if a quality of the first wirelessdata connection falls below a threshold quality measure.

A software application installed and running on mobile telephony devicemay configure the mobile telephony device to include some or all of theelements illustrated in FIG. 7. In alternate embodiments, a computerrunning a software application could configure the computer to includesome or all of the elements illustrated in FIG. 7. In still otherembodiments, other types of IP telephony devices could be configured toinclude some or all of the elements illustrated in FIG. 7.

FIG. 8 illustrates elements of a media relay communication system 800embodying the invention that is capable of performing methods embodyingthe invention. The media relay communication system 800 includes a datacommunications unit 802 that exchanges data packets bearing the media ofa VOIP telephone call with a mobile telephony device via one or morewireless data connections to the mobile telephony device. The mediarelay communication system also includes a verification unit 804 thatreceives a certificate for a particular call during initial call setup.The certificate could be received from a proxy server, from a telephonydevice that will participate in the call, or from some other elements ofthe IP telephony system. The verification unit also receivesverification communications sent from a mobile telephony device when themobile telephony device switches from a first wireless data connectionto a second wireless data connection. The verification communication issent over the new wireless data connection, and the verificationcommunication includes a copy of the certificate identifying the VOIPtelephone call. The verification unit 804 compares the originallyreceived certificate to the certificate received from the mobiletelephony device over the new wireless data connection. If thecertificates match, the data communication unit 802 exchanges datapackets bearing the media of the VOIP telephone call with the mobiletelephony device via the second wireless data connection.

A media relay could include software that configures the media relay toinclude some of all of the elements illustrated in FIG. 8. In alternateembodiments, some features may be present on one physical device,whereas other features may be present on another physical device, withthe elements operating together to provide all the elements illustratedin FIG. 8.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of communicating data packets bearingthe media of a voice over Internet protocol (VOIP) telephone call to andfrom a telephony device, comprising: preparing to exchange said datapackets with the telephony device through a first wireless dataconnection; receiving a communication from the telephony device througha second wireless data connection, the communication including acertificate identifying the VOIP telephone call; and exchangingsubsequent data packets bearing the media of the VOIP telephone callwith the telephony device through the second wireless data connection.2. The method of claim 1, wherein the steps are performed by a mediarelay.
 3. The method of claim 1, wherein the step of exchangingsubsequent data packets through the second wireless data connection isonly performed if the certificate received from the telephony devicethrough the second wireless data connection matches a previouslyreceived certificate for the VOIP telephone call.
 4. The method of claim1, further comprising exchanging data packets with the telephony devicethrough the first wireless data connection before the receiving andexchanging steps are preformed, wherein exchanging data packets with thetelephony device through the first wireless data connection comprisesreceiving data packets from and sending data packets to a first logicaladdress that includes an Internet protocol (IP) address and a portnumber, and wherein the step of exchanging subsequent data packets withthe telephony device through the second wireless data connectioncomprises receiving data packets from and sending data packets to asecond logical address that includes an IP address and a port number,wherein the first logical address is different from the second logicaladdress.
 5. The method of claim 1, wherein the preparing step comprisesreceiving a certificate identifying the VOIP telephone call.
 6. Themethod of claim 5, wherein the certificate identifying the VOIPtelephone call is received from the telephony device.
 7. The method ofclaim 5, wherein the certificate identifying the VOIP telephone call isreceived from a server that is setting up the VOIP call.
 8. The methodof claim 5, wherein the certificate identifying the VOIP telephone callis received during call setup and before data packets bearing the mediaof the VOIP telephone call are exchanged with the telephony device. 9.The method of claim 5, further comprising determining whether thecertificate received during the preparing step matches the certificatereceived from the telephony device through the second wireless dataconnection, wherein data packets bearing the media of the VOIP telephonecall are exchanged with the telephony device through the second wirelessdata connection only if the certificate received during the preparingstep matches the certificate received from the telephony device throughthe second wireless data connection.
 10. The method of claim 1, furthercomprising the steps of: exchanging data packets bearing the media ofthe VOIP telephone call with the telephony device through the firstwireless data connection before the receiving and exchanging steps arepreformed, receiving a certificate identifying the VOIP telephone callfrom the telephony device through the first wireless data connectionafter at least some data packets bearing the media of the VOIP telephonecall have been exchanged with the telephony device though the firstwireless data connection; and determining whether the certificatereceived through the first wireless data connection matches thecertificate received through the second wireless data connection,wherein data packets bearing the media of the VOIP telephone call areexchanged with the telephony device through the second wireless dataconnection only if the certificate received through the first wirelessdata connection matches the certificate received through the secondwireless data connection.
 11. The method of claim 1, further comprising:placing data packets received from the telephony device through thefirst wireless data connection in a data buffer; and sending datapackets stored in the data buffer to a telephony device which is a partyto the VOIP telephone call while the telephony device switches from thefirst wireless data connection to the second wireless data connection.12. The method of claim 11, further comprising: receiving a warningcommunication from the telephony device that indicates that thetelephony device may need to switch from the first wireless dataconnection to a different wireless data connection; and increasing asize of the data buffer in response to receipt of the warningcommunication.
 13. A system for communicating data packets bearing themedia of a voice over Internet protocol (VOIP) telephone call to andfrom a telephony device, comprising: means for preparing to exchangesaid data packets with the telephony device through a first wirelessdata connection; means for receiving a communication from the telephonydevice through a second wireless data connection, the communicationincluding a certificate identifying the VOIP telephone call; and meansfor exchanging subsequent data packets bearing the media of the VOIPtelephone call with the telephony device through the second wirelessdata connection.
 14. A system for communicating data packets bearing themedia of a voice over Internet protocol (VOIP) telephone call to andfrom a telephony device, comprising: a data communications unit thatexchanges said data packets with the telephony device through at leastone wireless data connection and that exchanges call setup signalingwith the telephony device through a first wireless data connection tothe telephony device; and a verification unit that receives averification communication sent from the telephony device through asecond wireless data connection to the mobile telephony device, whereinthe verification communication includes a certificate identifying theVOIP telephone call, and wherein the data communications unit exchangesdata packets bearing the media of the VOIP telephone call with thetelephony device via the second wireless data connection if the receivedcertificate matches a previously received certificate for the VOIPtelephone call.
 15. The system of claim 14, wherein the datacommunications unit exchanges data packets with the telephony devicethrough the first wireless data connection by receiving the data packetsfrom and sending the data packets to a first logical address thatincludes an Internet protocol (IP) address and a port number, and thedata communications unit exchanges data packets with the telephonydevice through the second wireless data connection by receiving the datapackets from and sending the data packets to a second logical addressthat includes an IP address and a port number, wherein the first logicaladdress is different from the second logical address.
 16. The system ofclaim 14, wherein the verification unit determines if the certificatesent from the telephony device through the second wireless dataconnection matches a certificate for the VOIP telephone call that wasreceived during call setup.
 17. The system of claim 14, wherein theverification unit determines if the certificate sent from the telephonydevice through the second wireless data connection matches a certificatefor the VOIP telephone call that was received from the telephony devicethrough the first wireless data connection.
 18. The system of claim 14,further comprising a data buffer for data packets bearing the media ofthe VOIP telephone call, wherein the data communications unit storesdata packets received from the telephony device in the data buffer. 19.The system of claim 18, wherein the data communications unit sends datapackets in the data buffer to a telephony device which is a party to theVOIP telephone call while the telephony device switches from the firstwireless data connection to the second wireless data connection.
 20. Thesystem of claim 18, wherein the data communications unit increases asize of the data buffer if the data communications unit receives awarning communication from the telephony device that indicates that thetelephony device may need to switch from the first wireless dataconnection to the second wireless data connection.